1. Field of the Invention
This invention relates to a trace lead analysis method, and in particular to a method of analyzing gasoline containing trace amounts of organolead or inorganic lead compounds.
2. Description of the Prior Art
The availability of unleaded gasoline to modern motorists is a subject of increased industrial effort among gasoline suppliers. The marketing operations for unleaded gasoline, however, involve shipment over present distributive facilities which also carry leaded gasoline. Accordingly, lead is still present in pipelines, tank cars, tank trucks, in service station pumps and reservoirs and the like. Coupled with this is a prospective governmental fine which may be exacted for failure of the gasoline supplier to keep the lead content in unleaded gasoline below a certain maximum, such as 0.05 grams per gallon. Accordingly, it would be advantageous to make rapid on-the-spot analyses of gasoline samples for lead which may have been picked up during shipment of the gasoline and to permit non-technical personnel to carry out these analyses.
It is known, in Pilloni et al, Anal. Chim. Acta, 35 (1966) pages 325-329, to produce complex colored products by reacting diethyllead ion with the monosodium salt of 4-(2-pyridylazo)-resorcinol. This reaction is carried out in a buffered solution and a pH of about 9. The ions were produced from diethyllead dichloride. Also, similar disclosure is made by Dagnall et al in Talanta, Vol. 12 (1965) pages 583-588. Reference is also made to the text of Shapiro and Frey, The Organic Compounds of Lead, John Wiley & Sons, New York (1968), in particular, pages 75, 77, 266 and 302, which mentions organolead salts and the reaction with chelates.
None of the aforesaid references discloses a single, rapid yet exact method of determining a range of concentrations of lead in trace amounts in gasoline.
U.S. application Ser. No. 371,338, filed on June 18, 1973 discloses and claims a method of rapid trace lead analysis for unleaded gasoline by forming lead iodides. The method described in the said copending application is very accurate, providing that the source of the lead is known. However, commercial lead alkyl mixtures contain various concentrations of the tetramethyllead, which is relatively slower to form halides. Thus, if the lead source were not known, some of the tetramethyllead content of the gasoline may not have been susceptible to analysis by the said process.